Adaptive balancing for battery management

ABSTRACT

A battery balancing system includes an energy balancing circuit. Multiple battery cells are coupled to the energy balancing circuit. A health assessment circuit is coupled to the multiple battery cells and configured to sense a state of health and a charge of each of the multiple battery cells. The balancing circuit switches energy between the multiple battery cells as a function of the sensed state of health and state of charge of each of the multiple battery cells to balance charge there between.

RELATED APPLICATION

This application claims priority to European Patent Office Applicationnumber 16203528.1 (entitled ADAPTIVE BALANCING FOR BATTERY MANAGEMENT,filed Dec. 12, 2016) which is incorporated herein by reference.

BACKGROUND

Batteries are a main source of energy for hybrid or electric vehicles,mobile radio stations, laptops and many other electronic devices.Concerns regarding environmental issues as well as the shortage ofLithium (Li) ore on Earth are the driving forces to maximizing theeffectiveness in using these batteries and not the least in extendingtheir life. In most of applications Li Ion batteries consists of matrixof cells connected in series and/or parallel. Each battery cell has itsown peculiarities. A battery cell state of health (SoH) is different dueto different aging, and therefore battery cell behavior in the pack willbe different.

State of health is a complex concept which includes monitoring thedegradation of the battery over time. The primary way that SoH isdetermined is by comparing the total capacity of the battery underconsideration to the capacity of a new battery, taking into account suchfactors as charge acceptance, internal resistance, voltage, andself-discharge rate.

To improve battery lifespan, manufacturers take pains to ensure that allcells of a battery are as similar as possible to each other in order toprevent cell imbalance. Generally, cell imbalance is when the SoC ofcells in a string are mismatched either due to inconsistent capacitiesor uneven initial SOC, resulting in either degraded pack performancerelative to the weakest cell or the abuse of the weak cell by theoperation of the rest of the pack. Since no two cells are exactlyidentical due to differences in SoC, self-discharge rate, capacity,impedance, and temperature characteristics' SoC divergence is a distinctpossibility within a string of cells.

Many batteries packs, particularly large strings with high power andfrequent cycling requirements, have a battery management system (BMS) tomonitor and protect against overcharge, over discharge, excessivecurrent rates, extreme temperatures, cell imbalance and other safetyfactors dependent on the battery chemistry. There are already developedBMS which perform active or passive cell balancing. In passivebalancing, current is directed around cells which are ‘full’—at 100%SOC—and shunted through resistors.

This method is very cheap to implement but not very effective atbalancing batteries with substantial variation in SoC, as well as beingwasteful of energy, as higher energy cells shed excess energy viaresistors, generating heat. However, one of the main purposes of a BMSis to prevent the loss of energy that could be stored, so while thismethod is good for protecting the health and lifespan of the battery itmay be undesirable depending on the application.

Conditioning charges may be considered to be a form of passivebalancing, since such charges serve that purpose. The use ofconditioning charges, however, is not particularly energy efficient assuch charges may typically utilize passive balancers functioning onlyduring the charge cycle.

Sorted by circuit topology there are three types of active balancers:the shunting method, the shuttling method, and the energy convertermethod. The shunting method is similar to the passive shunting methoddescribed above but instead of changing current flow immediately uponreaching a certain voltage for a given cell, the current isproportionally shunted away through resistors. The shuttling methodinvolves capacitive or inductive charge shuttling from cells with highSOC to cells with low SOC, and can be much more efficient for batterieswith frequent charge-discharge cycling. The energy converter method isdefined by some as isolated converters where the input and output sideof the converters have isolated grounds. However, the power wasted instandby may be greater for active balancing than for passive due toinaccurate measurements and switching phenomenon.

Further problems associated with active balancing include that balancingcannot be performed on adjacent cells at the same time. The switchesused to perform the balancing may also be exposed to highdrain-to-source voltage that exceeds what the switch can sustain.

SUMMARY

A battery balancing system includes an energy balancing circuit.Multiple battery cells are coupled to the energy balancing circuit. Ahealth assessment circuit is coupled to the multiple battery cells andconfigured to sense a state of health and a charge of each of themultiple battery cells. The balancing circuit switches energy betweenthe multiple battery cells as a function of the sensed state of healthand state of charge of each of the multiple battery cells to balancecharge there between.

A computer implemented method includes receiving state of health andstate of charge measurements for multiple cells of a multiple cellbattery, calculating an amount of energy to transfer between cells,determining switch controls of an energy balancing circuit responsive tothe calculated energy transfer, and controlling the switches to transferthe calculated amount of energy.

A device includes a processor and a memory device coupled to theprocessor and having a program stored thereon. The program is executableby the processor to receive state of health and state of chargemeasurements for multiple cells of a multiple cell battery, calculate anamount of energy to transfer between cells, determine switch controls ofan energy balancing circuit responsive to the calculated energytransfer, and control the switches to transfer the calculated amount ofenergy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block schematic diagram of an adaptive balancing controlsystem for a battery that includes multiple cells according to anexample embodiment.

FIG. 2 is a schematic diagram of an active balancing circuit accordingto an example embodiment.

FIG. 3 is a flowchart illustrating a method of adaptive balancingcontrol according to an example embodiment.

FIG. 4 is a graph illustrating an example impedance curve of animpedance spectroscopy measuring impedance characteristics of a batteryor cell of a battery according to an example embodiment.

FIG. 5 is a schematic diagram of an equivalent circuit of a batteryaccording to an example embodiment.

FIG. 6 is a graph illustrating an impedance curve generated from theequivalent circuit to verify a fitting between impedance curvesaccording to an example embodiment.

FIG. 7 is a graph illustrating an impedance curve of a model of theequivalent circuit of FIG. 5 according to an example embodiment.

FIG. 8 is a block schematic diagram of a battery system according to anexample embodiment.

FIG. 9 is a block schematic diagram of a computer system to implementcomponents of a smart adaptive balancing system according to a exampleembodiments.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings that form a part hereof, and in which is shown by way ofillustration specific embodiments which may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatother embodiments may be utilized and that structural, logical andelectrical changes may be made without departing from the scope of thepresent invention. The following description of example embodiments is,therefore, not to be taken in a limited sense, and the scope of thepresent invention is defined by the appended claims.

The functions or algorithms described herein may be implemented insoftware in one embodiment. The software may consist of computerexecutable instructions stored on computer readable media or computerreadable storage device such as one or more non-transitory memories orother type of hardware based storage devices, either local or networked.Further, such functions correspond to modules, which may be software,hardware, firmware or any combination thereof. Multiple functions may beperformed in one or more modules as desired, and the embodimentsdescribed are merely examples. The software may be executed on a digitalsignal processor, ASIC, microprocessor, or other type of processoroperating on a computer system, such as a personal computer, server orother computer system, turning such computer system into a specificallyprogrammed machine.

A smart adaptive balancing system may provide benefits to save energyand extend the lifetime of battery pack by maintaining cell balance, allof cells of a battery in an adaptive manner taking into considerationphenomenon which may occur due to the aging of battery.

The balancing system continuously monitors the status of each cell ofthe battery, identifies the parameters of each cell (SoH and SoC), andthrough a smart adaptive algorithm controls the delivery of the energyfrom the fully charged cells to the cells with a deficit of energy thusrealizing a balanced SoC for all cells consequently providing lifeextension for the battery pack as well as significant energy saving.

Correlating the SoH with the quantity of energy to be received by theless charged cells from the fully charged cells may be accomplishedusing a well- established transfer function which characterizes the SoHof the battery, to compare the calculated results with the measuredparameters of the battery and thus controls the charging of all theelements adapted to their state of charge and state of health.

In various embodiments, the system includes an electronic system whichmonitors the SoH and SoC status of battery cells through any of severalavailable methods (impedance spectroscopy, internal resistancemeasurement and/or charging discharging time measurement), an electricalcircuit which interconnects the batteries cells in a configuration whichgives the possibility of transferring the power from the cells withexceeding energy to the cell with deficit of energy in a controlledmanner. The system may provide wireless information to a vehicle driverand/or to the battery SoC monitoring center avoiding its prematureaging/destruction.

When the monitoring system detects that one specific cell presentsmodification of SoH will modify accordingly the modulation of chargetransfer from the other cells with a better SoH in a manner to avoidcharging it with high currents. In various embodiments, the system maycomprise an independent module installed on each battery pack. Themodule may be installed on the battery casing and may be re-used afterthe cells reach an end of life cycle, such as by replacing the cellswith new cells.

FIG. 1 is a block schematic diagram of an adaptive balancing controlsystem 100 for a battery that includes multiple cells. That battery inthis simple embodiment includes five cells that are indicated at 110,115, 120, 125, and 130, with labels CELL 1, CELL 2, CELL 3, CELL 4, andCELL 5 respectively. As indicated above, it is difficult to match cellsperfectly, such that their state of health is always the same. Thus,situations may arise where charging the cells results in CELL 1 beingcharted to 100%, CELL 2 to 110%, CELL 3 to 80%, CELL 4 to 90%, and cell5 to 110%. This is just one example of charges that may result from nobalancing occurring during charging. Similarly, when discharging occurs,such as the battery providing energy for a length of time, the cells maydischarge unevenly, resulting in respective charges of 0%, 20%, −10%, 0%and −10%. Overcharging and overdrained cells may further adverselyaffect individual cell state of health and lead to early end of life forthe entire battery.

A circuit 135 is used to perform both a health assessment and chargedetection in one embodiment. The health assessment may be performed byimpedance spectroscopy using a specialized integrated circuit (IC), suchas Analog Devices AD 350 in one embodiment. In further embodiments boththe SoH and SoC status of battery cells may be provided through any ofseveral available methods (impedance spectroscopy, internal resistancemeasurement and/or charging discharging time measurement).

A balancing circuit 140 is coupled to the cells and to the healthassessment and charge detection circuit. The balancing circuitdetermines what cells to transfer energy to and from via lines 145 and150, which provide suitable switching circuitry to transfer energy froma selected cell to another cell responsive to information provided bythe circuit 135 regarding SoH and SoC. The energy switching may occurany time during charging as well as discharging, and may take manyforms. In some embodiments, energy is transferred from the cell with thehighest charge to the cell with the lowest charge. In furtherembodiments, energy may be transferred from one or more cells with thehighest charge to one or more cells with lower charges.

In one embodiment, an active balancing circuit as shown at 200 in FIG. 2may be used to transfer energy between adjacent cells in a controlledmanner to avoid switching problems. Active balancing circuit 200 in oneembodiment is shown between a first cell 210 and a second cell 215. Afirst switch 220, Q1 is coupled in parallel with first cell 210 and asecond switch 225, Q2, is coupled in parallel with second cell 215. Thecells are coupled in series as represented by charge storage devices,capacitors 217 and 218 respectively such that their voltages add. Byutilizing capacitive or inductive charge shuttling between the cells,charge may be balanced. By controlling the first and second switches 220and 225 in accordance with measured SoC and SoH, the charge may beshuttled much more efficiently than in prior active balancing circuits.With Q1 on and Q2 off, current flows from CELL 1 to CELL 2 when CELL 2has a lower charge than CELL 1 as indicated by arrows 230 and 235. Inone embodiment, the current flows through a resistor 240 and inductor245 coupled in parallel.

The amount of charge to transfer may be determined by the balancingcircuit 140, which is broken into battery management system controller250 and an energy control 255. Inductor 245 stores an amount of energy,Q, which is stored in the inductance L of inductor 245. This energy istransferred from a battery such as battery 210 to another battery, suchas battery 215. In one embodiment, a coil of inductor 245 is wrapped ona ferrite core 260. An additional coil 265 is also magnetically coupledto the ferrite core 260 and is used to pre-magnetize the ferrite core260 by running current through coil 265 via energy control 255 ascontrolled by controller 250. This allows control via energy control 255of the amount of energy to be transferred via the inductor 245 inaccordance with the following equation:

${{Energy}\mspace{14mu} {stored}} = {{\int_{0}^{t}{P\ {dt}}} = {{\int_{0}^{I}{{Li}^{\prime}\ {di}^{\prime}}} = {\frac{1}{2}{{LI}^{2}.}}}}$

FIG. 3 is a flowchart illustrating a method 300 of adaptive balancingcontrol such as may be implemented by balancing circuit 140. At 310, SoHand SoC measurements are received from circuit 135. The measurement areused to calculate an amount or quantity of energy to be delivered to andfrom each cell at 315 without exceeding maximum and minimum charges foreach cell. At 320, charging and discharging charges are determined basedon the amount of energy to be delivered to and from each cell. Cellsthat have less charge than other cells generally are identified toreceive charge from cells that have more charge than other cells. Cellswith higher charge are identified and can provide more charge than cellswith lower charge.

In various embodiments, a table lookup may be used based on SoH and SoCto determine the charge to be transferred between two cells. At 325,switch controls are determined to accomplish the charge transfers. Theswitches are then controlled at 330 responsive to the determined switchcontrols to accomplish the charge transfers. The process may then berepeated based on SoH and SoC following the charge transfers, or in realtime as charge is being transferred, to adjust switch controls.

FIG. 4 is a graph 400 illustrating an example impedance curve 410 of animpedance spectroscopy measuring impedance characteristics of a batteryor cell of a battery. From the impedance measurements, an equivalentcircuit 500 of the battery or cell may be established as indicated inthe circuit diagram of FIG. 5. The equivalent circuit 500 includes aseries coupled resistor 510 and inductor 515. A further parallel coupledresistor 520 and capacitor 525 are also coupled in series with theresistor 510 and inductor 515. An impedance 530 and voltage 535 are alsocoupled in series with the prior electrical elements.

FIG. 6 is a graph 600 illustrating an impedance curve 610 generated fromthe equivalent circuit 500 to verify a fitting between the impedancecurves 410 and 610. A mathematical model of the equivalent circuit 500may then be generated, and example results of the model are shown inFIG. 7, which is a graph 700 illustrating an impedance curve 710 of themodel.

FIG. 8 is a block schematic diagram of a battery system 800 according toan example embodiment. Battery system 800 includes a controller 805 thatis coupled to multiple battery modules 810 to 815. Each module mayinclude one or more sub-modules such as indicated at 820, 825, 830, and835. Each sub-module may have multiple battery cells. The modules andsubmodules maybe coupled in any manner to provide desired batteryelectrical capabilities, including voltage and current capabilities.

In one embodiment, each module may have a balancing circuit as indicatedat 840 and 845 as well as health assessment circuit 850 and 855 capableof measuring SoH and SoC of each cell. The control system 805 mayreceive measurements from the health assessment circuits 850 and 855,and determine how much charge to transfer between the various cells. Thetransfers may take place between adjacent cells, cells in the samesub-module, cells in different submodules of the same module, and cellsin different modules in various embodiments, driven by the measured Sohand SoC of the various cells in order to optimize overall charge storageand life of the battery system 800 without exceeding maximum and minimumcharge limitations of each cell.

In various embodiments, a smart, adaptive, balancing system for (BMS)battery management system includes an electronic system which monitorsthe SoC of battery cells through any of available methods (impedancespectroscopy, internal resistance measurement and/or chargingdischarging time measurement), an electrical circuit which interconnectsthe batteries cells in a configuration transfer the power from the cellswith exceeding energy to the cell or cells with deficit of energy in acontrolled manner., and an electronic system which controls and commandsthe charge transfer from cell to cell.

In some embodiments, an electronic system provides a wireless linkbetween the battery management system and a battery monitoring centerand/or operator. In some embodiments, a method and algorithm providesbattery cell SoH detection and adaptive balancing control.

FIG. 9 is a block schematic diagram of a computer system 900 toimplement components of the smart adaptive balancing system, includingthe control system, and methods according to example embodiments. Allcomponents need not be used in various embodiments. One examplecomputing device in the form of a computer 900, may include a processingunit 902, memory 903, removable storage 910, and non-removable storage912. Although the example computing device is illustrated and describedas computer 900, the computing device may be in different forms indifferent embodiments. For example, the computing device may instead bea smartphone, a tablet, smartwatch, or other computing device includingthe same or similar elements as illustrated and described with regard toFIG. 9. Devices such as smartphones, tablets, and smartwatches aregenerally collectively referred to as mobile devices. Further, althoughthe various data storage elements are illustrated as part of thecomputer 900, the storage may also or alternatively include cloud-basedstorage accessible via a network, such as the Internet.

Memory 903 may include volatile memory 914 and non-volatile memory 908.Computer 900 may include—or have access to a computing environment thatincludes—a variety of computer-readable media, such as volatile memory914 and non-volatile memory 908, removable storage 910 and non-removablestorage 912. Computer storage includes random access memory (RAM), readonly memory (ROM), erasable programmable read-only memory (EPROM) &electrically erasable programmable read-only memory (EEPROM), flashmemory or other memory technologies, compact disc read-only memory (CDROM), Digital Versatile Disks (DVD) or other optical disk storage,magnetic cassettes, magnetic tape, magnetic disk storage or othermagnetic storage devices capable of storing computer-readableinstructions for execution to perform functions described herein.

Computer 900 may include or have access to a computing environment thatincludes input 906, output 904, and a communication connection 916.Output 904 may include a display device, such as a touchscreen, thatalso may serve as an input device. The input 906 may include one or moreof a touchscreen, touchpad, mouse, keyboard, camera, one or moredevice-specific buttons, one or more sensors integrated within orcoupled via wired or wireless data connections to the computer 900, andother input devices. The computer may operate in a networked environmentusing a communication connection to connect to one or more remotecomputers, such as database servers, including cloud based servers andstorage. The remote computer may include a personal computer (PC),server, router, network PC, a peer device or other common network node,or the like. The communication connection may include a Local AreaNetwork (LAN), a Wide Area Network (WAN), cellular, WiFi, Bluetooth, orother networks.

Computer-readable instructions stored on a computer-readable storagedevice are executable by the processing unit 902 of the computer 900. Ahard drive, CD-ROM, and RAM are some examples of articles including anon-transitory computer-readable medium such as a storage device. Theterms computer-readable medium and storage device do not include carrierwaves. For example, a computer program 918 may be used to causeprocessing unit 902 to perform one or more methods or algorithmsdescribed herein.

EXAMPLES

In example 1, battery balancing system includes an energy balancingcircuit. Multiple battery cells are coupled to the energy balancingcircuit. A health assessment circuit is coupled to the multiple batterycells and configured to sense a state of health and a charge of each ofthe multiple battery cells. The balancing circuit switches energybetween the multiple battery cells as a function of the sensed state ofhealth and state of charge of each of the multiple battery cells tobalance charge there between.

Example 2 includes the battery balancing system of example 1 wherein theenergy balancing circuit includes multiple switches controllable toroute energy between selected cells of the multiple battery cells.

Example 3 includes the battery balancing system of example 2 and furthercomprising a controller coupled to the energy balancing circuit and thehealth assessment circuit to determine an amount of charge to transferbetween cells and to control the switches to effect the determinedtransfer.

Example 4 includes the battery balancing system of example 3 wherein thehealth assessment circuit continuously senses the state of health andstate of charge of each battery cell and the controller continuouslyupdates switch settings.

Example 5 includes the battery balancing system of any of examples 3-4wherein the balancing circuit switches energy between the multiplebattery cells without exceeding minimum and maximum charges for eachcell.

Example 6 includes the battery balancing system of any of examples 3-5wherein the health assessment system comprises an impedance spectroscopycircuit.

Example 7 includes the battery balancing system of any of examples 3-6wherein the health assessment system comprises circuitry to perform aninternal resistance measurement to determine state of health of eachcell.

Example 8 includes the battery balancing system of any of examples 3-7wherein the health assessment system comprises circuitry to performcharging discharging time measurement to determine state of charge ofeach cell.

Example 9 includes the battery balancing system of any of examples 3-8wherein the multiple battery cells comprises a sub-module, and whereinmultiple sub-modules are coupled to form a module coupled to the energybalancing circuit and health assessment circuit.

Example 10 includes the battery balancing system of example 9 whereinthe balancing circuit is operable under control of the controller toswitch energy between cells of different sub-modules.

Example 11 includes the battery balancing system of example 10 andfurther comprising multiple additional modules coupled to thecontroller.

In example 12 a computer implemented method includes receiving state ofhealth and state of charge measurements for multiple cells of a multiplecell battery, calculating an amount of energy to transfer between cells,determining switch controls of an energy balancing circuit responsive tothe calculated energy transfer, and controlling the switches to transferthe calculated amount of energy.

Example 13 includes the computer implemented method of example 12wherein energy is transferred during charging or discharging of thecells.

Example 14 includes the computer implemented method of any of examples12-13 wherein the state of health and state of charge of each batterycell is continuously received and wherein the switches are continuouslycontrolled responsive to the continuously received state of health andstate of charge.

Example 15 includes the battery balancing system of any of examples12-14 wherein energy is switched between the multiple battery cellswithout exceeding minimum and maximum charges for each cell.

Example 16 includes the battery balancing system of any of examples12-15 wherein the received state of health and state of charge aremeasured by impedance spectroscopy.

In Example 17 a device includes a processor and a memory device coupledto the processor and having a program stored thereon. The program isexecutable by the processor to receive state of health and state ofcharge measurements for multiple cells of a multiple cell battery,calculate an amount of energy to transfer between cells, determineswitch controls of an energy balancing circuit responsive to thecalculated energy transfer, and control the switches to transfer thecalculated amount of energy.

Example 18 includes the device of example 17 wherein energy istransferred during charging or discharging of the cells.

Example 19 includes the device of any of examples 17-18 wherein thestate of health and state of charge of each battery cell is continuouslyreceived and wherein the switches are continuously controlled responsiveto the continuously received state of health and state of charge.

Example 20 includes the device of any of examples 17-19 wherein energyis switched between the multiple battery cells without exceeding minimumand maximum charges for each cell and wherein the received state ofhealth and state of charge are measured by impedance spectroscopy.

Although a few embodiments have been described in detail above, othermodifications are possible. For example, the logic flows depicted in thefigures do not require the particular order shown, or sequential order,to achieve desirable results. Other steps may be provided, or steps maybe eliminated, from the described flows, and other components may beadded to, or removed from, the described systems. Other embodiments maybe within the scope of the following claims.

1. A battery balancing system comprising: an energy balancing circuit;multiple battery cells coupled to the energy balancing circuit; a healthassessment circuit coupled to the multiple battery cells and configuredto sense a state of health and a charge of each of the multiple batterycells; and wherein the balancing circuit switches energy between themultiple battery cells as a function of the sensed state of health andstate of charge of each of the multiple battery cells to balance chargethere between.
 2. The battery balancing system of claim 1 wherein theenergy balancing circuit includes multiple switches controllable toroute energy between selected cells of the multiple battery cells. 3.The battery balancing system of claim 2 and further comprising acontroller coupled to the energy balancing circuit and the healthassessment circuit to determine an amount of charge to transfer betweencells and to control the switches to effect the determined transfer. 4.The battery balancing system of claim 3 wherein the health assessmentcircuit continuously senses the state of health and state of charge ofeach battery cell and the controller continuously updates switchsettings.
 5. The battery balancing system of claim 3 wherein thebalancing circuit switches energy between the multiple battery cellswithout exceeding minimum and maximum charges for each cell.
 6. Thebattery balancing system of claim 3 wherein the health assessment systemcomprises an impedance spectroscopy circuit.
 7. The battery balancingsystem of claim 3 wherein the health assessment system comprisescircuitry to perform an internal resistance measurement to determinestate of health of each cell.
 8. The battery balancing system of claim 3wherein the health assessment system comprises circuitry to performcharging discharging time measurement to determine state of charge ofeach cell.
 9. The battery balancing system of claim 3 wherein themultiple battery cells comprises a sub-module, and wherein multiplesub-modules are coupled to form a module coupled to the energy balancingcircuit and health assessment circuit.
 10. The battery balancing systemof claim 9 wherein the balancing circuit is operable under control ofthe controller to switch energy between cells of different sub-modules.11. The battery balancing system of claim 10 and further comprisingmultiple additional modules coupled to the controller.
 12. A computerimplemented method comprising: receiving state of health and state ofcharge measurements for multiple cells of a multiple cell battery;calculating an amount of energy to transfer between cells; determiningswitch controls of an energy balancing circuit responsive to thecalculated energy transfer; and controlling the switches to transfer thecalculated amount of energy.
 13. The computer implemented method ofclaim 12 wherein energy is transferred during charging or discharging ofthe cells.
 14. The computer implemented method of claim 12 wherein thestate of health and state of charge of each battery cell is continuouslyreceived and wherein the switches are continuously controlled responsiveto the continuously received state of health and state of charge. 15.The computer implemented method of claim 12 wherein energy is switchedbetween the multiple battery cells without exceeding minimum and maximumcharges for each cell.
 16. The computer implemented method of claim 12wherein the received state of health and state of charge are measured byimpedance spectroscopy.
 17. A device comprising: a processor; and amemory device coupled to the processor and having a program storedthereon for execution by the processor to: receive state of health andstate of charge measurements for multiple cells of a multiple cellbattery; calculate an amount of energy to transfer between cells;determine switch controls of an energy balancing circuit responsive tothe calculated energy transfer; and control the switches to transfer thecalculated amount of energy.
 18. The device of claim 17 wherein energyis transferred during charging or discharging of the cells.
 19. Thedevice of claim 17 wherein the state of health and state of charge ofeach battery cell is continuously received and wherein the switches arecontinuously controlled responsive to the continuously received state ofhealth and state of charge.
 20. The device of claim 17 wherein energy isswitched between the multiple battery cells without exceeding minimumand maximum charges for each cell and wherein the received state ofhealth and state of charge are measured by impedance spectroscopy.